Reactive management will always be needed because, simply, failure happens. Devices unexpectedly fail, changes turn out to have unintended consequences, backhoes cut fiber, or entire electrical grids go down. Reactive management is the most demanding from a time perspective because administrators have no prior warning and still must assemble their resources and attack the problem as best they can.
Components of reaction time include the following:
Problem detection and verification, initiated by the instrumentation and refined by the management tools
Problem isolation, consisting of further analysis to identify and isolate the cause of any (potential) service disruption
Problem resolution, in which steps are taken to resolve ...